The overall objective of this project is to compare the efficacy of two different treatments for idiopathic sudden sensorineural hearing loss (SSNHL). SSNHL is an otologic emergency causing unilateral deafness of variable severity. If treated promptly with a short course of oral corticosteroids, approximately 60% of patients regain some hearing. However, in patients with severe-to-profound SSNHL it is rare to fully recover hearing. Increasing duration of oral steroid therapy beyond three to four weeks has never been shown to improve hearing outcome, and the risk of steroid side effects rises with greater duration of treatment. Recent animal studies of corticosteroid penetrance into the inner ear and reports of treatment outcome in several small uncontrolled series of SSNHL patients suggest that local administration of corticosteroids by intratympanic (IT) injection may achieve equivalent or better hearing recovery while lowering the potential risk of systemic side effects. In this project we propose a multicenter prospective randomized clinical trial to compare the efficacy of oral prednisone vs. IT methylprednisolone for primary treatment of SSNHL. All qualified subjects will be randomized to receive either two weeks or oral prednisone or two weeks of IT methylprednisolone injections. The two Specific Aims of the study are to: (1) test the primary hypothesis that IT corticosteroids are as effective as oral prednisone for primary SSNHL treatment; and (2) compare the side-effects and adverse events in subjects treated with oral or IT steroids. The project is designed as an equivalency study. If the primary hypothesis of equivalency is supported, results of the second Specific Aim, comparison of side-effects, will guide clinical practice. If the two treatments are not equivalent, the study design enables us to detect which is better and by how much. Thus the results of this study will have significant impact on evidence-based clinical practice guidelines for management of SSNHL. This application is for the collaborating Clinical Coordinating Center (CCC).